The present invention relates to a battery using an anode active material containing tin (Sn), cobalt (Co), and carbon (C) as an element.
In recent years, many portable electronic devices such as a combination camera (Videotape Recorder), a mobile phone, and a notebook personal computer have been introduced. As downsizing and weight saving of such devices have been made, improving energy density of the battery used as a portable power source for such electronic devices, particularly of the secondary battery has been strongly demanded.
As a secondary battery to meet such a demand, so-called lithium ion secondary batteries using a graphite material utilizing intercalation reaction of lithium ions, or using a carbon material applying insertion and extraction action of lithium ions to and from the fine pores for the anode active material have been traditionally in practical use.
However, in recent years, as technical advancement of portable equipment has been made, demand for capacities of secondary batteries has become stronger. As a secondary battery to meet such a demand, it has been suggested that a light metal such as a lithium metal is used as it is as an anode active material. In such a battery, in the process of charging, the light metal is easily dendrite-precipitated on the anode, and the current density becomes very high at the end of the dendrite. Therefore, there have been disadvantages that the cycle life is deteriorated due to decomposition of the nonaqueous electrolytic solution or the like, or dendrite is excessively grown to cause internal short circuit of the battery.
Meanwhile, using various alloy materials or the like as an anode active material has been suggested. For example, in Japanese Unexamined Patent Application Publication Nos. H07-302588, H10-199524, H07-326342, H10-255768, and H10-302770, descriptions are given of silicon alloys. Further, in Japanese Unexamined Patent Publication No. H04-12586, Japanese Unexamined Patent Application Publication Nos. H10-308207, S61-66369, S62-145650, H10-125317, H10-223221, S10-308207, and H11-86854, descriptions are given of tin-nickel alloy, lithium-aluminum-tin alloy, tin-zinc alloy, a tin alloy containing phosphorus (P) in the range from 1 wt % to 55 wt %, Cu2NiSn, Mg2Sn, tin-copper alloy, or a mixture of a tin containing phase inserting lithium and a phase not inserting lithium (Li) including manganese (Mn), iron (Fe), cobalt, nickel (Ni), or copper (Cu).
However, even in the cases using such alloy materials, it is a reality that sufficient cycle characteristics are not able to be obtained, and advantages of the high capacity anodes in the alloy materials are not sufficiently utilized.
Therefore, as an anode active material capable of sufficiently improving cycle characteristics, a material containing tin, cobalt, and carbon as an element has been developed. However, there is a shortcoming that when a battery is actually manufactured, battery characteristics are not able to be improved without optimizing the surface density ratio to the cathode active material layer.